Vehicle evaporative emissions control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. In an effort to meet stringent federal emissions regulations, emission control systems may need to be intermittently diagnosed for the presence of undesired evaporative emissions that could release fuel vapors to the atmosphere.
Undesired evaporative emissions may be identified using engine-off natural vacuum (EONV) during conditions when a vehicle engine is not operating. In particular, a fuel system may be isolated at an engine-off event. The pressure in such a fuel system will increase if the tank is heated further (e.g., from hot exhaust or a hot parking surface) as liquid fuel vaporizes. As a fuel tank cools down, a vacuum is generated therein as fuel vapors condense to liquid fuel. Vacuum generation is monitored and undesired evaporative emissions identified based on expected vacuum development or expected rates of vacuum development. The EONV evaporative emissions test may be monitored for a period of time based on an available battery charge.
However, the EONV test is prone to false failures based on customer driving and parking habits. For example, a refueling event that fills the fuel tank with relatively cool liquid fuel followed by a short ensuing trip may fail to heat the fuel bulk mass and result in a false fail if an EONV test is run. Further, the rates of vacuum development are based in part on the ambient temperature. During mild weather conditions, the ambient temperature may restrict the amount of heating or cooling of the fuel tank following engine shut-off, and thus limit the rate of pressure or vacuum development. As such, vacuum may not reach expected threshold levels in the time allotted for the EONV test based on available battery charge. This may result in a false-fail condition, leading to potentially unnecessary engine service.
U.S. Pat. No. 9,140,627 teaches a method for a vehicle fuel system comprising indicating whether an ambient temperature is within a threshold range, and if so, operating a cooling fan to increase a fuel tank vacuum, and indicating undesired evaporative emissions in the vehicle fuel system based on the increased vacuum. However, the inventors herein have recognized potential issues with such a method. For example, U.S. Pat. No. 9,140,627 teaches conducting the evaporative emissions test procedure during engine off conditions, where operating a cooling fan may negatively impact vehicle battery charge capacity, and may thus in turn negatively impact fuel consumption.
Thus, the inventors herein have recognized the above issues, and have developed systems and methods to at least partially address the above issues. In one example, a method is provided comprising responsive to an indication that a vehicle is in the process of a car wash event; sealing a fuel system and an evaporative emissions system of the vehicle; and conducting a diagnostic test for the presence of undesired evaporative emissions.
As one example, the fuel system includes a fuel tank that supplies fuel to an engine of the vehicle, and the evaporative emissions system includes a fuel vapor canister configured to capture and store fuel vapors from the fuel tank, and wherein sealing the fuel system and evaporative emissions system comprises sealing the fuel system and evaporative emission system from atmosphere and from the engine, and wherein a fuel tank temperature decrease during the car wash event results in a vacuum build in the fuel system and evaporative emissions system. In this way, during a car wash event where the vehicle fuel tank is likely to be rapidly cooled as a result of cold water striking the fuel tank, the fuel system and evaporative emissions system may be sealed and the presence or absence of undesired evaporative emissions indicated based on a vacuum build in the fuel system and evaporative emissions system. By conducting an evaporative emissions test diagnostic based on conditions where a vacuum build in the fuel system and evaporative emissions system is likely to be robust, test completion rates may be improved, and undesired evaporative emissions may be reduced.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.